Inhibited fuming nitric acids



INHIBITED FUMING NITRIC ACIDS Karl F. Hager, Clearfield, Pa., and William R. Lucas and Douglas B. Franklin, Huntsville, vAla, assignors to the United States of America as representedby the Secretary of the Army No Drawing. Filed June 25, 1957, Ser. No. 668,283

v I '14 Claims. (Cl. 52.5)

( Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties thereon. V

The present invention relates to the protection of metals against acid attack. In particular, this invention relates to novel concentrated nitric acid fuel oxidizer compositions and to a method for the protection of ferrous metals and ferrous metal alloys from the eifect produced by the. action of such nitric acid fuel oxidizers in contact therewith, by incorporating in such fuel oxidizers small amounts of pyridine, quinoline, substituted quinolines and other N-heterocylic compounds containing more than one benzene ring.

Fuming nitric acid fuel oxidizers, some types and descriptionsof which may be found in Patent No. 2,573,471, issued October 30, 1951, to Malina et al., are known to be among the more important oxygen. carriers used in modern rocketry. However, because these nitric acids are also among the most corrosive of oxidizing acids,

- one of the major limitations involved in the use of fuming nitricv acid propellant fuel oxidizers is the extreme reactivity of such fuels with the metals most commonly used for fuel and storage tank purposes.

This condition of reactivity, therefore, makes it difiicult to choose appropriate materials for the construction of storage tanks, fuel tanks, etc., which will withstand extended periods of exposure to these acids. Pure aluminum, for instance, is relatively resistant to fumingnitric acids and is suitable for storage tank use, but its mechanical strength makes it unsuitable for use at rocket fuel tanks. Steel tanks lined with aluminum would be suit able for use as storage tanks, but would be impractical and uneconomical for expendable fuel tank use. 7 Again, certain stainless steels possess the proper physical properties for rocket fuel tank construction as well as the desired resistance to these acids, but these are not always readily available such as, for instance, in the event of a national emergency; Furthermore, fuming nitric acids form objectionable sludges when in contact with some stainless steels considered resistant to these acids. Other ferrous metals and alloys thereof usually have the requisite physical properties, but the excessive rate of acid attack on these .mctals and alloys makes their use for rocketry purposes unadvisable.

cheaper and more readily obtainable than stainless steel. Most of the known inhibitors of acid attack on metals are useless in the case of fuming nitric acids since they From the economic standpoint then, it is desirable to use a steel which is 2,981,617 Patented Apr. 25, 1961 are chiefly organic compounds which are chemically sensitive to the oxidizing action of the fuming nitric acids.

Very few inorganic inhibitors have beenproposed for turning nitric acid retardation (inhibition), and those known to be in use act by plating the ferrous surfaces With a nobler metallic film which is not sufficiently resistant to the fuming nitric acids for the above purposes.

I alloysthereof from acid attack.

An additional object of this invention is to provide a new and novel method whereby the detrimental acid attack produced by fuming nitric acids in contact with ferrous metals and metallic alloys thereof is substantially inhibited. Other objects of this invention will in part be obvious and will in part appear herein.

Experience has shown that for the purposesspecified herein the material to be in contact with these fuming nitric acids should not be attacked corrosively to a degree higher than .001 inch penetration per year. Stainless steels, the most resistant ofthe ferrous metals, are usually attacked corrosively more an .004 inch penetrationper year (i.p.y.) when in contact with fuming nitric acids.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation.

EXAMPLE I inhibitor added to the acid in this series of tests'was 8- nitroquinoline. In each'series of tests of the following examples, at least one control specimen (not inhibited) was included so that a comparison could be made between the rate of attack of the inhibited versus the un-, inhibited acid under corresponding conditions. The rate of acid attack was checked by determining the weight loss of the specimen at regular intervals. .In preparation for weighing, the specimens were removed from the acid, rinsed with water, and dried. After weighing, the dry specimens were returned to the acid. In this case, the specimens were weighed after three days and at weekly or biweekly intervals thereafter until 101 days'ela'psed. The retardation of the acid attack was calculated as follows:

Percent retardation= weight loss of uninhibited wt loss of inhibitedX Wt. loss of uninhibited V The data are presented in Table I.

' I 'FUMLNG NITRIC ACID 7 1 addedtheretoi as theinhibitor 0.5%: by weight).

Table I WEIGHT PERCENT, WEIGHT LQSSOF SAE 4130, STEEL H1903, 6.5% N02, 3.1% H) with. 8-hydroxyqninoline At I I i I I Tests were conducted in the; same manner and under I I I v I itheisame conditions as in ExampleI. In .thiscase, 'SAE. I

' I I I I 4130 steel I was: stored in turning nitric .acid: (90.3%

7 I the end of 63 days, the weightless of the. inhibited sam pic was 46 milligrams per, square decimeter per: day I I V (m.d.d.) as compared with 160 m.d.d. for the uninhibited 1 specimen.

The'retardation at'the' endof 63 days was,

Tests were conducted in the same manner and under I t the: same conditions as in Example I'except that in this 7 case; various concentrations of 8-hydroxyquinoline were, I .I I added to diiferent I test bottles of fuming nitric acid I I (90.18% iHNO 7.23% N0 2.59% H O). At the end I of 101 days, the weight loss of a specimen of 4 l'steel in acid inhibited with 1.0% of 8-hydroxyquinoline by: weight was only 48.2 m.d.d. as compared with 166 m.d.d.

. for the uninihibited sample, a retardation of 71.0%. The

retardation was 90% after 49 days of storage. A concentration of 0.5% of S-hydroxyquinoline showed a retardation of 91.0% after 18 days, but dropped to 57.7% after 101 days. A concentration of 0.25% 8-hydroxyquinoline gave a retardation of 36.6% at the end of 101 days.

EXAMPLE IV EXAMPLE V A series of similar tests to those of Example I were conducted with SAE 1010 steel, fuming nitric acid (90.18% HNO 7.23% N0 2.59% H 0) and 8-hydroxyquinoline added as the inhibitor. (0.5 by weight). After 18 days, the weight loss of the specimen in the inhibited acid was only 28 m.d.d, as compared with 1706 I m.d.d. for the specimen in the uninhibited acid (98.4% retardation). After 101 days, the retardation was still 80%.

EXAMPLE VI Tests similar to those of Example I were conducted in which AISI 316 stainless steel specimens were immersed in diiferent bottles containing fuming nitric acid (89.74% HNO 7.68% N0 2.58% H O) with 8-hydroxyquinoline added to some bottles and 8-nitroquino- 'At the end of 13' days, the: retardation was I I Control 1.0% 0.5% .0025% Time, days mg/om." mdd. nag/elm. rndd. Percent i:ng';.,'dm. mdd. Percent mgJdm. rndd., I Percent ret. ret ret.

199 v66 7 5. 2 1. 4 97.4 I 8. 1 2. 7 96. 0 130 4 3. 3 35. 2 931 93 4.6 0.5 99.5 7.7 0.8 I 99.2 '559 I 55.9 40.2 1, 687 99 3. 7 0. 2 99. 8 7. 4 0. 4 99. 6 1, 096 64. 5 85. 3 479 I 103 I 6. 6 0. 3 99. 7 10.9 0. 5 99. 6 1, 738 72. 4 30.2 3,199 103 7. 9 O. 3 99. 8 12. 0 0. 4 '99. 6 2, 211 71. 3 31.0 3, 764' 99 8.3 0.2' 99. 13.1. 0.3 I 99.7 2,660 69. 9"v 29.6 4,478 97 9. 9 0. 2 99.8 15. 5 0. 3 99. 7 3, 222 70. 0. 28. 3 4, 966 10. 7 0. 2 99. 8 17. 3 0. 3 99. 7 3, 628 69. 3, 27.3 5,669 95 12.9 0.2 99.8 19.9 0.3 99.7 4,203 70.0 26.2 6,929 94 14.2 0.2 99.8 28. 2 0.4 99.6 5,276 71.3 24.2 7,983 92 16.2 0.2 99.8 43.5 0.5 99.5 6,232 71.6 I 22.3 9,026 89 20.8 0.2 99.8 68.1 0.7 99.2 7,163 70.9 21.0 a

' I Milligrams per square decimeter. I

' I "Milligrams per square declmeter per day. I I I I I I I I I I v I v EXAMPLE II 20 line added to other bottles as inhibitors. At the end of 45 days, the specimen in acid to which 1.0% 8-hydroxymen in the fuming nitric acid to which 1.0% :8-nitro- I quinoline was added, lost only 0.04 m.d.d; in 45 days,- I I i I and a 0.5 addition of the same inhibitor allowed a I i weightless of only 0.2 m.d.d.;

itardationwas over 99%; I I I i ,EXAMPLEVIL, I Other tests similar to Examplel were; conducted to checktheeflectivenessofthese inhibitors with AISI 347 stainless .steel. I The, acid concentration for these tests was as'followsi 90.06% HNO 76% N02, 2.34% H O. i I p In 45 days, a specimen in'acidinhibited with 1.0% 8- I V l hydroxyquinoline lost only 2.7;m.d.d. whereas, a speci- I 7 men in uninhibited acid lost 93 m.d.d. I A specimen in I acid inhibited with. 0.5 8-hydroxy'quinoline lost 15 I i I m.d.d. 7 :Weight loss of specimens in acid inhibited with I 8-nitroquinoline was somewhat'less 'When 1.0% 8-nitro-' I quinoline was added to the acid, the weight loss of the specimen was 0.8 m.d.d. and 1.8 m.d.d. when 0.5% 8-nitroquinoline was added to the acid.

EXAMPLE VJII Tests were conducted under the same condition and in the same manner as Example I in which SAE 1010 steel was stored in different containers of turning nitric acid (90.07% HNO 7.55% N0 2.36% H O) to which varied amounts of 8-hydroxyquinoline or 8-nitroquinoline were added to the different bottles. With each inhibitor, the concentrations Varied from 1.0%, to 0.1%, After 45 days, the corrosion of specimens in the acid inhibited with 1.0% of S-hydroxyquinoline was retarded to the extent of 98.2%, and 0.1% 8-hydroxyquinoline gave a retardation of 74.4%. the above limits gave results between the retardation figures given above. The retardation resulting from an addition of 1.0% 8-nitroquinoline was 99.7% at the end of 45 days, and in the same period of time 99.6% retardation was obtained from an addition of 0.5% of the same inhibitor. The corresponding values were 98.9% from 0.25% 8-nitroquinoline, 76.3% from 0.1% 8-nitroquinoline, and 52% from 0.025% nitroquinoline after 45 days.

EXAMPLE IX Specimens of SAE 1010 steel were placed in containers of fuming nitric acid (90.71% HNO 7.35% N0 1.94% H 0) inhibited with different compounds. which are related chemically to the two compounds used in previous examples. The weight loss of a specimen in acid .inihibited with 1.0% quinoline was retarded by 98.2% after 10 days, and a 0.5% addition of quinoline gave a retardation of 93.7% during the same period of and, in both cases,the re-. j I I Concentrations between specimen in the acid inhibited with acridine was only 13.4 m.d.d. whereas the weight loss of an uninhibited specimen was 1415 m.d.d,

EXAMPLE X Tests were conducted in the same manner and under the same conditions as in Example I in which SAE 1010 steel was stored in diflierent containers of fuming nitric acid (91.00% HNO 6.56% N0 2.44% H O), one container inhibited with 0.5% and the other container inhibited with 0.25% of 6,8-dim'troqninoline. After days the corrosion of specimens in the acid inhibited with 0.5% 6,8-dinitroquinoline exhibited a loss of only 20.5 m.d.d. or 91.2% retardation. That inhibited with 0.25% of 6,8-dinitroquinoline exhibited a loss of 033.1 m.d.d. or an 85.75% retardation. Tests conducted with 2-hydroxyquinoline in concentrations of 0.5% and 0.25% exhibited 89.7% and 77.0% retardation respectively under similar test conditions. 7-hydroxyquinoline in concentrations of 0.5% and 0.25% exhibited 98.3% and '96.1% retardation respectively under similar test con ditions. All the above results were based on the examination of the metal samples after a 10-day period.

EXAMPLE XI In order to show that these inhibitors are elfective with other concentrations of the fuming nitric acids, tests similar to those of Example I were conducted using technical grade red fuming (80.01% HNO 17.83% N0 1.36% H 0) and technical grade white fuming (94.32% HNO 2.61% N0 3.07% H O) nitric acids. The addition of 0.5 S-nitroquinoline to the white fuming nitric acid had retarded the attack of the acid on SAE 1010 steel by 95.5% at the end of 10 days. The addition of 1.0% of S-nitroquinoline to the red fuming nitric acid had retarded the attack of the acid on SAE 1010 steel by 98.5% at the end of 10 days.

The foregoing examples are intended merely as illustrations of our invention. Sincemodifications in the examples will occur to those skilled in the art, we wish to be limited,-not.by the scope of the specific-examples, but solely by the appended claims.

We claim: I

l. The liquid fuel composition consisting essentially of nitric acid of the group consisting of red fuming Nostrand Company, Inc., New York (1953), page 489;

nitric acid and white fuming nitric acid to which has been added a maximum of 1% of an organic compound of the class consisting of 8-nitroquinoline, 8-hydroxyquinoline, S-nitroquinoline, 6,8-dinitroquinoline, 7-hydroyxyquinoline, and 2-hydroxyquinoline to inhibit the corrosion of ferrous metal surfaces.

- 2. The fuel composition of claim 1 in which the inhibitor additive is S-nitroquinoline.

3. The fuel composition of claim 1 hibitor additive is 8-hydroxyquinoline.

4. The fuel composition of claim 1 hibitor additive is S-nitroquinoline.

5. The fuel composition of claim 1 hibitor additive is 6,8-dinitroquinoline.

6. The fuel composition of claim 1 hibitor additive is 7-hyclroxyquinoline.

7. The fuel composition of claim 1 hibitor additive is 2-hydroxyquino1ine.

8. The method of protecting ferrous metal surfaces from the corrosive action produced thereon by a liquid fuel mixture consisting essentially of nitric acid from the group consisting of red fuming nitric acid and white fuming nitric acid in contact therewith, which comprises contacting said fuel mixture with the metal surface in the presence of a maximum of 1% of an organic compound of the class consisting of S-nitroquinoline, 8- hydroxyquinoline, S-nitroquinoline, 6,8-dinitroquinoline, 7-hydroxyquinoline and 2-hydroxyquinoline.

9. The method of claim 8 in which the inhibitor additive is 8-nitroquinoline. i I

10. Themethod of claim 8 in which the inhibitor additive is S-hydroxyquinoline.

11. The method of claim 8 in which the inhibitor additive is S-nitroquinoline.

12. The method of claim 8 in which the inhibitor additive is 6,8-dinitroquinoline.

13. The method of claim 8 in which the inhibitor additive is 7-hydroxyqninoline.

14. The method of claim 8 in which the inhibitor additive is 2-hydroxyquinoline.

References Cited in the file of this patent UNITED STATES PATENTS in which the inin which the inin which the inin which the inin which the in- 2,053,024 Dreyfus Sept. 1, 1936 2,068,868 Pier et al. Ian. 26, 1937 2,499,283 Robinson Feb. 28, 1950 2,573,471 Malina et al. Oct. 30, 1951 OTHER REFERENCES The Van Nostrand Chemists Dictionary, D. Van 

1. THE LIQUID FUEL COMPOSITION CONSISTING ESSENTIALLY OF NITRIC ACID OF THE GROUP CONSISTING OF RED FUMING NITRIC ACID AND WHITE FUMING NITRIC ACID TO WHICH HAS BEEN ADDED A MAXIMUM OF 1% OF AN ORGANIC COMPOUND OF THE CLASS CONSISTING OF 8-NITROQUINOLINE, 8-HYDROXYQUINOLINE, 5-NITROQUINOLINE, 6,8DINTROQUINOLINE, 7-HYDROYXYQUINOLINE, AND 2-HYDROXYQUINOLINE, TO INHIBIT THE CORROSION OF FERROUS METAL SURFACES. 